1. Field of Invention
The present invention relates to a process of recovery and reuse of textile sizes. More particularly, it relates to the recovery of interpolymers of C.sub.4 to C.sub.7 vinyl esters and .alpha., .beta.-unsaturated acids from woven goods and reuse of the interpolymers as a warp size.
2. Prior Art
In textile weaving, warp yarn is sized with an aqueous solution of a water soluble polymer and is then woven with the woof into cloth on a loom equipped with a mechanical shuttle or a water jet. The size forms on the surface of the warp yarn a coating or film which protects the yarn from abrasion and covers up warp defects such as knots, crossed ends, slubs and similar weak spots. The size must be abrasion resistant and adhere strongly to the yarn so that little shedding occurs during slashing and weaving of the yarn. When the yarn has been woven into cloth, the size is removed in a scouring bath containing an appropriate solvent for the size.
Preferred sizes are applied as aqueous solutions and are removed with water or aqueous solutions containing surfactants. Among the preferred sizes are interpolymers containing acid groups which provide solubility in aqueous solutions of bases such as alkali metal hydroxides and carbonates or ammonium hydroxide. Typical of such interpolymers are those acidic vinyl ester interpolymers disclosed in U.S. Pat. Nos. 3,723,381 and 3,759,858.
Traditionally, the textile industry has disposed of the dilute solutions of warp size formed in the scouring bath by dumping them into local sewage systems where their demand for chemical oxygen impairs the efficiency of effluent treatment, or into the lakes and streams where they may impose an intolerable biochemical oxygen demand on the life supporting medium of aquatic life. A need to avoid such pollution by removal of the textile size from wash solutions is not recognized.
The prior art teaches processes for recovery of acid interpolymers comprising ethylene and acrylic acid from the scouring solution by acidification of the solution to a pH in the range 4-6 to precipitate the polymer. While such polymers are readily recovered, they suffer from shortcomings which make their use as textile sizes undesirable. For example, they require a high acid content and an excess of strong base such as sodium hydroxide for solubility in aqueous media. Consequently, their solutions have a high pH, are hazardous to handle, and tend to break down wool fiber structure and to mercerize cotton yarns, both at the sizing and the desizing steps. Moreover, such sizes adhere poorly to yarns of polyester and polyester-cotton blends.
Textile sizes of acidic vinyl ester interpolymers generally adhere well to a broad spectrum of textile fibers and are effective sizes. However, recovery of such sizes by the processes of the prior art may be attended with hydrolysis of the vinyl ester groups, modifying the solution characteristics of the sizes and militating against the reuse of the sizes. Moreover, because of the hydrophilicity of the interpolymers in the acid form, precipitation of the size from the scouring solution tends to yield a gummy mass of interpolymer or an extremely finely divided interpolymer so that economic recovery becomes well nigh impossible. Thus, there exists a need in the art for a process of recovery of textile sizes of acidic vinyl ester interpolymers and a process of recovery and reuse of such interpolymers as textile sizes.